Depending on what your problem is, you could try ionic liquids, for inspiration take a look at these:
https://doi.org/10.1002/adma.200900603
https://doi.org/10.1002/anie.201100904
https://doi.org/10.1039/C3CE41203B
However, there are mainly two things to keep in mind. First, ionic Liquids are extremely versatile, with billions of possible systems. You thus need to put thought into the choice of your ions. If you just randomly buy "an ionic liquid", it will most likely fail to meet your purpose. After all, noone just buys "a solvent", it makes a difference if you use, say, THF or gasoline.
Second, working with ionic liquids is an art for itself that requires some expertise. If you are new to this field, pay particular attention to purity. Many studies using ionic liquids fail due to or are biased by impurities such as water or residual halides.
Dear Pengjun Zhao, manganese carbonate is insoluble in water, ammonia solution, and all organic solvents. Of course, it will dissolve in aqueous acids, but then it's not manganese carbonate any more...
Dera Rossen Buyukliev, I don't think this will dissove the MnCO3. A SciFinder search for the research topic "crown ether complexes of transition metal carbonates" revealed zero results.
MnCO3 is insoluble in organic solvents. So, I would like to suggest you to perform the reactions in mixture of solvents like THF:EtOH:Water in different ratios or else as suggested by Prof. F. T. Edelmann using aqueous acids or with Ionic liquids.
Dear Pengjun Zhao and Krishna Reddy when I mentioned dissolving MnCO3 in aqueous acids it was more like a joke. MnCO3 will certainly dissolve easily e.g. in nitric acid, but then you don't have MnCO3 any more but a solution of Mn(NO3)2.
Dear all, a similar question have been discussed years ago on RG, see link below. The attached file shows that its preparation in ethylene glycol. My Regards
Dear Abdelkader BOUAZIZ, thanks for providing the link and the reference! The attached article clearly confirms what I keep saying. MnCO3 can be prepared in ethylene gycol, because the precursor MnCl2 is soluble in coordinating organic solvents. However, the thus prepared MnCO3 precipitates from the reaction mixture, because it is insoluble in any organic solvents.